Posted by **Anonymous** on Wednesday, February 22, 2012 at 4:36pm.

Given that cos2x=7/12 and "270 equal or < 2x equal or < 360", find sinx.

Please help and Thank you

- Trig Help -
**Reiny**, Wednesday, February 22, 2012 at 5:06pm
In these type of quesstions it usually asks for the "exact" value of ....

cos 2x = 7/12

cos 2x = 1 - 2sin^2 x

2 sin^2 x = 1 - cos 2x = 1 - 7/12 = 5/12

sin^2 x = 5/24

sin x = √(5/24)

but 270 < 2x ≤ 360

135 ≤ x ≤ 180 ---> x in in I or II, so

sinx = +√5/√24 = √30/12

- Trig Help -
**Anonymous**, Wednesday, February 22, 2012 at 5:49pm
how did you get the 30/12?

- Trig Help -
**Anonymous**, Wednesday, February 22, 2012 at 6:15pm
sqrt(5)/2sqrt(6)

when you rationalize the denominator you times both top and bottom by sqrt(6) only not the 2 right?

## Answer this Question

## Related Questions

- trig - how do you solve: find cos2x if sinx is equal to 1/5
- Trig - I'm confused on how to determine what the end result angles are for a ...
- Math Help - Hello! Can someone please check and see if I did this right? Thanks...
- trig - cotx = -2 and 0 less than or equal to x less than or equal to pi Find ...
- Calculus - In the interval (0 is less than or equal to x which is less than or ...
- Trig Help - Prove the following: [1+sinx]/[1+cscx]=tanx/secx =[1+sinx]/[1+1/sinx...
- trig - 1/sinx = sinx+cosxcotx it's a proof and I have to make them equal to each...
- Trig (Last URGENT) - sin2x+cosx=0 , [-180,180) = 2sinxcosx+cosx=0 = cosx(2sinx+1...
- trig - sinx = 4/5 and x terminates in Quadrant II Find sin2x and cos2x How to ...
- Math - Solving Trig Equations - Solve each equation for o is less than and/or ...

More Related Questions